1. Field of the Invention
The present invention relates to a surface roughness measuring unit and a coordinate measuring apparatus. More specifically, the present invention relates to a surface roughness measuring unit that can be attached to and used with a coordinate measuring apparatus.
2. Description of Related Art
A coordinate measuring apparatus is known for measuring a three-dimensional contour shape of a work piece (for example, Japanese Patent Laid-open Publication No. 2006-201105).
The coordinate measuring apparatus includes a measurement head having at a tip of a stylus a contact ball that makes contact with a work piece, a moving mechanism moving the measurement head three-dimensionally in X, Y, and Z-axis directions, and a host computer measuring and recording the movement of the measurement head. An example of a known measurement head is a touch probe that outputs a touch signal when a contact ball is pushed into a work piece by a certain amount.
There is also a case where surface roughness such as minute unevenness and undulation (may be referred to as surface texture) on a work piece surface is an object of measurement. Japanese Patent Laid-open Publication No. H11-190621 discloses a surface texture measuring device. The surface texture measuring device disclosed in Japanese Patent Laid-open Publication No. H11-190621 includes a contact pin unit that has a contact pin displaceable in a direction perpendicular to a work piece surface and a driver that moves the contact pin unit forward and backward along the work piece surface.
The contact pin unit includes the contact pin that measures a surface texture represented by surface roughness and a displacement detector that detects displacement of the contact pin. The surface texture measuring device moves the contact pin unit forward and backward along the work piece surface with the driver, and detects displacement of the contact pin at this time with the displacement detector. The surface texture measuring device then converts the displacement to an electric signal, and performs predetermined processing of the electric signal to obtain a measured value of roughness of the work piece surface.